Method of making wire matrix print head nozzle

ABSTRACT

A dot matrix printing head nozzle structure and method of manufacturing such structure wherein a plurality of holes are formed in a block of plastic material using permanent and removable inserts. The holes are provided for receiving printing elements which are arranged to be as near perpendicular to the record medium as possible consistent with the size of the armature needed to drive the printing elements. The removable insert serves the additional function of providing an antiwicking region along the inserted wires to control undesirable ink flow along the wires when the nozzle is used for printing through an inked ribbon.

United States Patent Bittner METHOD OF MAKING WIRE MATRIX PRINT HEAD NOZZLE Inventor:

Assignee:

Filed:

Appl. No.: 493,974

John R. Bittner, Waynesboro, Va.

General Electric Company Aug. 1, 1974 US. Cl. 29/433; 29/423; 29/434;

Int. Cl 323p 19/04 Field of Search 29/433, 434, 157 C, 527.1,

29/423; l97/l R; 264/279, 275, 334, 317

References Cited UNITED STATES PATENTS Bonfiglio 29/604 July s, 1975 Assistant ExaminerVictor A. DiPalma [5 7 ABSTRACT A dot matrix printing head nozzle structure and method of manufacturing such structure wherein a plurality of holes are formed in a block of plastic material using permanent and removable inserts. The holes are provided for receiving printing elements which are arranged to be as near perpendicular to the record medium as possible consistent with the size of the armature needed to drive the printing elements. The removable insert serves the additional function of providing an antiwicking region along the inserted wires to control undesirable ink flow along the wires when the nozzle is used for printing through an inked ribbon.

4 Claims, 7 Drawing Figures PATENTEH JUL 8 I975 SHEET F l G I TO RESPECTIVE EL E CTROMAGNE TS FIG.2

l I I I I 1 I l I I I I I l l 32: I I I PATENTEHJUL 9 ms .3 8 93; 220

SHEET 2 FIGZA.

METHOD OF MAKING WIRE MATRIX PRINT HEAD NOZZLE BACKGROUND OF THE INVENTION The present invention relates to dot matrix printing apparatus and more particularly to an improved dot matrix printing nozzle and method of manufacturing such nozzle.

ln the so called dot matrix printer, visual characters are formed by groups of dots imprinted on paper. Each dot is produced by driving an impact end of an elongated printing element against the platen with the paper and an inked ribbon disposed between the printing element and the platen. Commonly, a plurality of printing elements are arranged in parallel to form a line transverse to the direction of travel of the paper. As the paper and printing elements are driven relative to one another, the dots are produced in successive parallel rows, one row at a time, by selectively actuating drivers which cause the printing elements to extend and retract according to the characters to be printed. Typical of this class of printers is the apparatus disclosed in French Pat. No. 2,094,311 entitled Improvements in Printing Heads for Printing machines" allowed January 10, 1972 in the name of LogAbax, S.A., US. Pat. 3,672,482 entitled Wire Matrix Print Head" issued in the name of Phillip Brumbaugh et al dated June 27, 1972 and U.S. Pat. 3,467,232 entitled Dot Printing apparatus issued in the name of W. G. Paige dated Sept. 16, 1969.

In a dot matrix printer, provision must be made for selectively actuating the printing elements to imprint the dots on the paper. The actuating mechanisms are of necessity located in the vicinity of their respective elements. Thus spaces occupied by the actuating mechanisms place a limit on the distance between the parallel printing elements in a line and, accordingly, the size of the characters. In one prior art arrangement, in order to provide space for the element actuators and achieve suitable driving forces, the actuators were arranged in an arc and the printing elements extended essentially radially from spaced points on the arc, following individual curved paths to the ends of the printing elements which were extended to impact on the record medium. Other prior art arrangements have provided the actuators in the form of solenoids which were mounted coaxially with the printing elements. This meant that the wires at the driving end had to be separated by at least the diameters of the actuators which were substantial. Both of these approaches offered significant disadvantages. The former resulted in excessive friction loading and wear of the printing elements resulting in reduced life. The latter resulted in character irregularities occasioned by the wide angular separation of the pring wires or elements which irregularities were accentuated by a misalignment of the head relative to the recording medium. Both of these arrangements also resulted in bulky designs which adversely affected performance particularly in the case where the print head was moved rapidly across a line on a record medium, such as paper.

Need exists therefore to provide an arrangement which minimizes misalignment of the wires at the print medium during the printing operation, maximizes the stiffness of the printing elements along the wire during impacting, and reduces the friction and wear and sticking of print wires while minimizing overshoot during a printing operation. Patent 2,094,311, cited above, attempted to accomplish this by resorting to the use of electromagnetically operated hinged armatures arranged in a circular array centered on the print wires with the actuator ends of the elements aligned substantially towards the center of the array in order to more adequately achieve the perpendicularity of the printing elements to the record medium. This invention, however, required the use of oval cross-section coils with the electromagnets spaced along the periphery of a circle. This arrangement, while a step in the desired direction, did not achieve the degree of perpendicularity de sirable and required an oval coil shape which is more difficult and costly to fabricate.

Patent application Ser. No. 423,779 entitled Wire Matrix Print Head filed Dec. 11, 1973 in the name of Seymour Merritt DePuy describes an improved print head design. The dot printing head comprises a nozzle including a plurality of elongated, axially extendable printing elements. the ends of each of the printing elements are juxtaposed to lie in a straight line in a plane parallel to the record medium. Means are provided at the other end of each of said printing elements for connection to or joining one end of a respective hinged armature which is driven by an associated electromagnet. Each armature is driven about a print axis by a respective electromagnet. The electromagnets are mounted about the periphery of an annular frame with the junctions of the printing elements and the associated armature ends positioned at spaced points along an oval locus of minimum circumference in a plane substantially perpendicular to the locus of the driven wires. This enables circular coils to be utilized for providing the driving action and enables a near perpendicularity of the printing elements to the record medium during the extension and retraction of the individual printing elements. For further details reference can be made to this application.

Print head nozzles have been manufactured wherein the print wires are guided between a wire driving means such as solenoids and the record medium by being imbedded in solid plastic which is molded around the Wires. In attempting to manufacture a print head nozzle with a complicated arrangement of the print wires in the region between the wire driving source and the record medium problems are encountered. If the wires are misaligned during the manufacturing, this leads to undesirable stresses which manifest themselves in wire breakage, wire jamming and improper printing. An arrangement is needed which maintains wire alignment during manufacturing as well as during printing, enables proper wire operation without jamming or sticking, which lends itself to low cost and repeatability of design in manufacture. Also it is desirable that the end product not unduly obscure the record medium during printing and prevent observation of the printing progress. Furthermore, where printing involves use of an inked ribbon it is desirable to minimize the undesirable flow of ink along the print wires into the region where they are being guided while providing means for guiding the ribbon in close proximity to where the wires exit from the nozzle.

Accordingly, it is one object of the present invention to provide a wire print head nozzle of improved design and a method for manufacturing the same.

A further object of this invention is to provide an easily manufactured, reliable, low cost print head nozzle which can affect the printing function adequately at high speeds.

Another object of the invention is to provide an improved method of manufacturing a print head nozzle employing wire alignment inserts during manufacture at least one of which inserts are removable to provide an antiwicking region along the print wires near the printing ends thereof.

Another object of the invention is to provide a method of molding a print nozzle to accommodate a relatively complex arrangement of print wires.

Another object is to provide an improved method and means for enabling printing by a wire print head nozzle without unduly obscuring visual observation of printing progress.

A further object is to provide an improved method and means for guiding ribbon around a print head nozzle tip without undue stressing of the ribbon and with minimal obscuring of printing progress.

Still another object of this invention is to provide an improved means for printing and a method of manufacture thereof.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I shows in side cross-sectional form certain de tails of the present nozzle invention as applied to a print head assembly.

FIG. 2 is a diagramatic sketch showing a top view of the nozzle with a schematic representation of the mold, gguides and inserts used in manufacturing the nozzle.

FIGS. 2A, 2B and 2C are schematic sectional views taken along the lines as shown in FIG. 2.

FIG. 3 shows the end of the print head nozzle where the printing elements extend to cause printing by impact through an inked ribbon.

FIG. 4 represents an enlarged view illustrating the manner in which the printing elements are juxtaposed to one another in a straight line at the printing end of the print head nozzle.

Referring to FIG. 1 of the drawings, it will be seen that a print head such as that employing a nozzle of the present invention comprises an actuator frame 1 on which there are supported a plurality of electromagnetically operated hinged armatures 2 for driving respective printing elements or wires 3. The wires are normally maintained in a non-print position or retracted position and when electively extended drive a printing ribbon such as, for example, an inked or carbon ribbon 4 into printing contact with a record medium 5 such as paper which is positioned in front of a platen 6. In one embodiment such a print head comprises seven print wires or printing elements 3 each of which is connected at its driven end 24 by connection to the end of a respective movable armature 2 associated with an electromagnet 25. Normally the armature 2 is maintained against the backstop 26 by operation of a spring hinge 7 which connects the armature to the frame 1 by means of screws or rivets l8. Backstop 26 may be a threaded part for adjustability, supported on an annular ring 22 which is attached to and spaced from frame 1 by through bolts 23 not shown. In this position the associated printing element 3 is maintained in its retracted position. In a particular application a printer responds to operation of a key in a keyboard or from data transmitted from a data source to produce a plurality of control signals from source 9 for selectively driving individual ones of the printing elements 3 to produce a graphical display of a desired symbol on a record medium. This is shown by block 9 which produces control signals over respective leads 10 coupled to associated electromagnet 25. As used here, lead 10 involves a two conductor line. For purposes of simplicity. the other leads 10 are merely shown with arrowheads going to respective coils. Assuming control signal source 9 produces a signal over lead 10, this causes the associated electromagnet 25 to overcome the bias force established by spring 7 and causes the armature to move to the right causing the associated print wire 3 to extend itself into printing contact with the inked ribbon to cause a dot to be graphically produced on the record medium 5. The duration of the signals available on 10 are a fraction of a millisecond such that following impact the field established by electromagnet 25 collapses and the biasing spring 7 operates to quickly draw the associated printing element into its retracted position. Depending upon the symbols involved, various combinations of the control signals on 10 cause the corresponding combinations of print wires to be extended to cause printing and then retracted to produce the desired matrix pattern. In one particular embodiment the print head was mounted on a carriage assembly for lateral movement across the line on a record medium.

As previously mentioned it is desirable to arrange the printing elements 3 and the armatures 2 to insure that the printing elements 3 are as near perpendicular to the record medium 5 as possible, consistent with the size of the armature needed at its junction with the printing elements. The advantages of approaching this desired perpendicular configuration is that it tends to minimize misalignment of the wires at the point where they impact against the record medium during a printing operation. In addition, if the wires 3 are maintained essentially straight along their length, this maximizes the stiffness of the printing elements or the wire during impact and reduces the friction and wear and sticking of the print wires by minimizing overshoot during a printing operation. As described in greater detail in the aforementioned copending application, these desirable objectives of perpendicularity at the point of impact and straightness of the print wires along their length had heretofore not been adequately met because of the inability of locating the actuators, at the point where they attach to the print wires, in a central location.

The desirable objectives of perpendicularity and straightness along their length is achieved with printing elements 3 by resorting to the use of electromagnetically operated hinged armatures. Each armature 2 as sociated with a respective electromagnetic actuator or coil 25 is positioned to extend inward toward a central location from which the printing elements or wires may be directed essentially perpendicularly to the record medium. The print wires engage the armature 2 and are attached thereto by the element 11 which would be a ferrule, screw or rivet, etc. Each of the junctions of the printing wire and its associated armature lie on spaced points in an oval located in a plane. The significance of this will be explained shortly. The impact ends of the print wires 3 exit from the print head nozzle at 12 as hown in FIG. 4. Normally an inked ribbon is caused to r iic the nozzle end I2 for engagement by the print wires 3 during a printing operation. FIG. 4 shows in greater detail how the various print wires exit from the print head. It will be seen that the wires are juxtaposed such that they are essentially contiguous to one another in a straight line. This line represents a row of possible dots. As the print head moves along a line on the record medium by selected energization, the various printing elements can then establish dot patterns in the form of symbols determined by the control signals available from 9 in FIG. 1. To guide the wires with minimum friction between their junction with the actuator 2 and the point at which they exit from the head for printing, print head nozzle 13 is shown to be of a molded plastic. In the particular embodiment, the plastic used was a self-lubricating acetal plastic. Because the departure from perpendicularity and straightness has been minimized by the present arrangement, friction forces encountered and the wear and sticking of print wires is minimized.

In order to control the lay of the various print wires from their attachment to respective driving armatures at one end to where the print wires exit from the print head nozzle to impact the record medium, the following method of manufacturing is employed. Referring to FIG. 2, the plastic nozzle 13 is shown comprising a driving end flange 27 which is to be used for mounting to the driving armatures shown in FIG. 1. At the other end the nozzle comprises a planar tip 12 on the nozzle end nearest where printing is to take place. The wires at the flange end are positioned at space points along an oval locus located in a first plane which is substantially parallel to the record medium 5. The wires exit from the nozzle at the tip end 12 at space points along a straight line locus substantially parallel to the record medium. At cross-sectional positions 28, the wires still retain their positioning along space points along an oval locus in a plane substantially parallel to the record medium but wherein the locus is of reduced size as compared to the wire spacing at the driven end. At cross-section point 2C, the wires are positioned at space points along a straight line locus in a plane substantially parallel to the record medium. Thus the problem arises of producing holes in a block of plastic corresponding to the nozzle configuration 13 wherein the holes proceed from being positioned at space points along an oval locus in a first plane to space points positioned along an oval locus of reduced size at a second plane to being positioned at space points along a line in a third plane to where they exit from the nozzle at tip 12 at space points along a straight line locus in a fourth plane where all of the planes are substantially parallel to one another.

To accomplish this manufacturing method, Applicant proposes to mold the plastic around core wires comprising a driving end guide 28, first insert 29, a sec ond insert 30 and a driven end guide 31. The guides 28 and 31 and inserts 29 and 30 comprise the fixtures used during the molding process to make the wires conform to the particular lay desired in order to achieve the most desirable printing operation. For purposes of simplicity FIG. 2 includes sections 2A, 2B and 2C which illustrate schematically the positioning of the holes around the respective loci in planes which are parallel to one another. Thus the driving end guide 28 has a fixture arranged such that the wire holes are provided for supporting core wires at one end thereof whereas the driven end guide 31 is provided with holes around its particular locus to define the other end position of the core wires when inserted into the mold and prior to the molding operation. To cause the wires to conform to the desired lay, insert 29 is provided with its fixture arranged to receive core wires in the holes shown in an oval locus of smaller size whereas insert 30 is shown comprising holes for receiving core wires in position along a straight line locus. In a normal procedure, the mold would be opened and the core wires inserted between the driving end guides and the driven end guides. Inserts 29 and 30 would then be in position to receive the core wires. The core wires are then threaded through the holes in guides 28 and 31 and inserts 29 and 30. The core wires are chosen to be slightly larger in diameter than the print wires to be actually used in the finished nozzle assembly. The particular embodiment of the core wires was selected to be a circular cross-section having a diameter of 0.016 inches whereas the actual print wires which were inserted into the holes left by the core wires were selected to have a diameter of 0.014 inches. After the core wires have been assembled, the mold is closed and liquid plastic under pressure is forced into the mold causing the plastic to flow around the wires between the driven end and driving end guides and around the inserts filling the entire cavity around the wires in this manner. Without the inserts 29 and 30 the high pressure fluid plastic would cause the wires to depart from their desired lay. After the fluid plastic has flowed around the wires and, in accordance with the process it has cooled, the mold is opened and the molded nozzle with the inserted core wires is removed. In a preferred embodiment insert 29 was selected to be a permanent insert which was molded in place in the nozzle. On the other hand, insert 30 was selected to be a removable insert. The purpose of this will be described in greater detail later. At this point there exists a molded nozzle assembly with inserted core wires which have been molded into a desired configuration. Removing the insert 30 leaves a cavity as shown in FIG. I. Potentially then there exists a region in the molded assembly where the core wires are unsupported by the plastic for a portion of their length in the region where the core wires were shielded by the second insert during the molding operation. By selecting the second insert to be near where the print wires emerged to cause printing, an antiwicking function is provided. Any ink flowing from ribbon 4 which would tend to flow along the wires by capillary action would encounter the cavity. The capillary activity would be terminated and the undesirable ink flow minimized. In the absence of such feature, problems have been encountered where the ink flowing along the print wires interfered with the proper movement of the wires in the holes formed in the plastic nozzle. In a preferred embodiment the plastic chosen was acetal as previously mentioned. This plastic has certain lubricative properties such that the combination of the lubricative property of the plastic enclosure for the wires coupled with the antiwicking device results in relative trouble free printing.

It will be recalled that the first insert 29 had openings in it positioned on an oval locus located in a plane. Because of this complex configuration of holes, the insert is made a permanent part of the molded nozzle after being used to hold or support the core wires in place during the molding operation. In one embodiment the insert was made of plastic similar to that used in the molding operation. The process is so arranged that the relatively cool insert does not collapse during the molding operation when the hot plastic is injected. To improve the visibility afforded the operator of a printer for which a nozzle such as the present one is employed,

the core wires are located such that the resulting holes are located at one side of said nozzle tip as shown in FIG. 3 closest to where the previous character would be printed on a record medium. This produces a minimal visual obscuring of printing progress. In order to minimize the stresses formed in the printing ribbon as it passes over the tip of the nozzle, there is provided a curved ribbon guide portion 32 which extends from the holes in a direction opposite to where the previous character would be printed. In this manner maximum observation of printing is provided with a minimum stressing of ink ribbon as it passes over the nozzle tip.

While in a preferred embodiment the core wires were removed prior to removing the second insert 30 and the actual print wires of reduced cross-section inserted to provide the print nozzle with wires, the alternative arrangement would be to provide the insert 30 of such a design that it could be removed as part of the molding operation, then with the nozzle removed from the molding fixture the core wires could be withdrawn and the print wires substituted therefor.

From the above description and the accompanying drawings it will be realized that l have provided a simple and effective wire matrix print head nozzle which minimizes misalignment of the wires at the record medium during the printing operation, maximizes the stiffness of the printing elements along the wire during impacting and reduces the friction and wear and sticking of print wires while minimizing overshoot during a printing operation. A print head embodying the principles of my invention is relatively inexpensive and easy to manufacture while retaining close operating tolerances. Uniform and stable operation of the print head nozzle is easily obtained.

While the invention has been particularly shown and described with reference to preferred embodiments thereof, it will be evident to those skilled in the art that various changes in form and detail may be made without departing from the spirit and scope of the invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

l. A method for manufacturing a wire matrix print nozzle wherein said nozzle comprises a block of plastic material with a plurality of holes extending throughout its length from a wire driving end to a wire driven end and adapted for receiving a plurality of elongated print wires for sliding movement therein such that the ends of the wires at their driven ends can impact a record medium through an inked ribbon comprising:

a mold having a wire driving end guide and a wire driven end guide, said driving end guide having wire holes positioned at space points along an oval locus in a first plane,

said driven end guide having wire holes positioned at spaced points along a line in a second plane substantially parallel to said first plane,

locating a first insert, having wire holes positioned at spaced points along an oval locus, intermediate said guides and with the plane of such locus substantially parallel to said first plane,

locating a second insert, having wire holes positioned at spaced points along a straight line locus, intermediate said first insert and said driven end guide and with the plane of such locus substantially parallel to said first plane,

inserting core wires between said guides such that each core wire is positioned in a respective hole in a driving end guide, passes through a respective hole in said first insert, passes through a respective hole in said second insert and is positioned in a respective hole in said driven end guide,

causing plastic to be molded around the wires and between said guides and to said first insert,

and removing said second insert from the molded plastic to leave unsupported by plastic that portion of the length of each core wire shielded by the second insert during the molding operation thereby providing an antiwicking region for minimizing ribbon ink flow in the holes of the nozzle.

2. An arrangement according to claim 1 further comprising the step of removing said core wires from said molded plastic and substituting therefore print wires of a diameter slightly less than the diameter of the holes remaining following removal of such core wires.

3. An arrangement according to claim 2 further com prising adding an antiwicking agent in the antiwicking region to further minimize ribbon ink flow along the print wires in the holes in the print nozzle.

4. An arrangement according to claim 3 further comprising the step of molding a planar tip on the nozzle end nearest the driven end guide, the nozzle holes being located at one side of said tip closest to where the previous character would be printed on a record medium to produce minimal visual obscuring of printing progress and a curved ribbon guide extending from the holes in a direction opposite to where the previous character would be printed.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION PATENT NO. I 3,893,220

DATED July 8, 1975 INVENTOMS) I John R. Bittner It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 1, line 55 cancel "pring" and insert print Signed and Scaled this Fourteenth D a )1 Of September 197 6 [SEAL] ANCSI.

RUTH C. MASON C. MARSHALL DANN Arresting ()jfirer (nmmr'ssimrvr njParenls and Trademarks 

1. A method for manufacturing a wire matrix print nozzle wherein said nozzle comprises a block of plastic material with a plurality of holes extending throughout its length from a wire driving end to a wire driven end and adapted for receiving a plurality of elongated print wires for sliding movement therein such that the ends of the wires at their driven ends can impact a record medium through an inked ribbon comprising: a mold having a wire driving end guide and a wire driven end guide, said driving end guide having wire holes positioned at space points along an oval locus in a first plane, said driven end guide having wire holes positioned at spaced points along a line in a second plane substantially parallel to said first plane, locating a first insert, having wire holes positioned at spaced points along an oval locus, intermediate said guides and with the plane of such locus substantially parallel to said first plane, locating a second insert, having wire holes positioned at spaced points along a straight line locus, intermediate said first insert and said driven end guide and with the plane of such locus substantially parallel to said first plane, inserting core wires between said guides such that each core wire is positioned in a respective hole in a driving end guide, passes through a respective hole in said first insert, passes through a respective hole in said second insert and is positioned in a respective hole in said driven end guide, causing plastic to be molded around the wires and between said guides and to said first insert, and removing said second insert from the molded plastic to leave unsupported by plastic that portion of the length of each core wire shielded by the second insert during the molding operation thereby providing an antiwicking region for minimizing ribbon ink flow in the holes of the nozzle.
 2. An arrangement according to claim 1 further comprising the step of removing said core wires from said molded plastic and substituting therefore print wires of a diameter slightly less than the diameter of the holes remaining following removal of such core wires.
 3. An arrangement according to claim 2 further comprising adding an antiwicking agent in the antiwicking region to further minimize ribbon ink flow along the print wires in the holes in the print nozzle.
 4. An arrangement according to claim 3 further comprising the step of molding a planar tip on the nozzle end nearest the driven end guide, the nozzle holes being located at one side of said tip closest to where the previous character would be printed on a record medium to produce minimal visual obscuring of printing progress and a curved ribbon guide extending from the holes in a direction opposite to where the previous character would be printed. 